The objectives of the proposed research are to understand the pathogenesis of diffuse renal diseases in man (glomerulonephritis, nephrotic syndrome and tubulointerstitial nephritis) by a comprehensive immunopathologic study of: the role of local glomerular factors on immune complex localization in the capillary wall and in the glomerular mesangium, the effects of immunologic and biochemical injury to the glomerulus on mesangial uptake and transport of macromolecules, the kinetics and physiologic consequences of distal tubular in situ immune complex formation mediated by antibodies to Tamm-Horsfall protein. The methods employed will include renal transplantation and renal perfusion in rats, and quantitative macromolecular tracer, biochemical, radioisotope, immunologic and immunopathologic techniques.